The switch statement could be added to the hasCondition matcher.
Example:
clang-query> match switchStmt(hasCondition(ignoringImpCasts(declRefExpr())))
Output:
Match #1: Binding for "root": SwitchStmt 0x2f9b528 </usr/local/google/home/etienneb/examples/enum.cc:35:3, line:38:3> |-<<<NULL>>> |-ImplicitCastExpr 0x2f9b510 <line:35:11> 'int' <IntegralCast> | `-ImplicitCastExpr 0x2f9b4f8 <col:11> 'enum Color' <LValueToRValue> | `-DeclRefExpr 0x2f9b4d0 <col:11> 'enum Color' lvalue Var 0x2f9a118 'C' 'enum Color' `-CompoundStmt 0x2f9b610 <col:14, line:38:3> |-CaseStmt 0x2f9b578 <line:36:3, col:22> | |-ImplicitCastExpr 0x2f9b638 <col:8> 'int' <IntegralCast> | | `-DeclRefExpr 0x2f9b550 <col:8> 'enum Size' EnumConstant 0x2f99e40 'Small' 'enum Size' | |-<<<NULL>>> | `-ReturnStmt 0x2f9b5d0 <col:15, col:22> | `-IntegerLiteral 0x2f9b5b0 <col:22> 'int' 1 `-DefaultStmt 0x2f9b5f0 <line:37:3, col:12> `-BreakStmt 0x2f9b5e8 <col:12> 1 match.